help with this maths question ( decorator-energetic/lazy )

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pndt.snl
Posts: 35
Joined: Tue Oct 05, 2010 2:13 pm

help with this maths question ( decorator-energetic/lazy )

Post by pndt.snl »

Pl help with this question-

It takes 2 decorators 8 days to paint a house.
One is lazy and one is energetic.
Energetic can paint the whole house in 12 days on his own.
How many days would it take lazy to paint the house on his own?

Thanks ...
Tagore
Posts: 121
Joined: Thu Jun 14, 2012 10:28 am

Re: help with this maths question ( decorator-energetic/lazy

Post by Tagore »

pndt.snl wrote:Pl help with this question-

It takes 2 decorators 8 days to paint a house.
One is lazy and one is energetic.
Energetic can paint the whole house in 12 days on his own.
How many days would it take lazy to paint the house on his own?

Thanks ...
If the energetic one paints the whole house in 12 days, then he paints 8/12= 2/3 of the house in 8 days. Thus, the lazy paints 1/3 of the house in 8 days (since both of them working together complete the job in 8 days). It follows then it would take the lazy one 24 days to paint the whole house on his own.
T
mystery
Posts: 8927
Joined: Tue Jul 21, 2009 10:56 pm

Re: help with this maths question ( decorator-energetic/lazy

Post by mystery »

I'm sure there are lots of ways to think about it, but this is my method. Let's say the area of the house is A.

Energetic must paint A/12 per day because he can complete the job in 12 days on his own.

Say Lazy's amount per day is L.

We know that 8 x Lazy's amount per day + 8 x energetic's amount per day = A

This is because we are told that together they can paint the whole house in 8 days

So 8 L + 8 x A/12 = A

If you re-organise this you get that L = A/24

This tells you that Lazy can paint 1/24th of the house on his own each day. So it would take him 24 days on his own to paint the whole house.
Last edited by mystery on Thu Sep 20, 2012 11:10 am, edited 1 time in total.
mystery
Posts: 8927
Joined: Tue Jul 21, 2009 10:56 pm

Re: help with this maths question ( decorator-energetic/lazy

Post by mystery »

Our posts crossed! Your way is neater. In the heat of an exam I'd do it my way because my formal algebra sticks but my reasoning goes! Every child is different.
pndt.snl
Posts: 35
Joined: Tue Oct 05, 2010 2:13 pm

Re: help with this maths question ( decorator-energetic/lazy

Post by pndt.snl »

Thank you so much.
Really appreciate it !!
mystery
Posts: 8927
Joined: Tue Jul 21, 2009 10:56 pm

Re: help with this maths question ( decorator-energetic/lazy

Post by mystery »

Sorry there was a typo in my workings which I have just edited. I hope I didn't cause any confusion.
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